Field of the Invention
This invention relates to a method of manufacturing a sliding bearing in which a first member and a second member are combined together relatively movably, such as, for example, a spherical bearing in which a ball portion and a holder are connected together rotatably or swingably, and a linear guide appratus in which a track shaft and a slider are combined together slidably, and more particularly to a method of manufacturing a sliding bearing of the type in which a resin liner is interposed between such first and second members.
Japanese Patent Publication No. 42569/1976 discloses a spherical bearing in which an inner race and an outer race are combined together rotatably or swingably via a resin liner. To be concrete, this spherical bearing includes an inner race provided with a convex surface as a sliding guide surface, a resin liner of a low friction coefficient covering the convex surface of this inner race, and an outer race covering the convex surface of the inner race via this resin liner. Since the resin liner and inner race fixed to each other are in sliding contact with the outer race, these inner and outer races are combined together rotatably or swingably.
In this spherical bearing, the outer race is molded by die casting with the inner race used as a core, the inner race being thereby sealed in an inner portion of the outer race. Namely, a resin liner formed cylindrically in advance is put on the convex surface of an inner race member, and the resultant product is thereafter set as a core in a metal mold, a pressurized molten metal, such as a zinc alloy, an aluminum alloy and the like being poured with the core left in this condition into a cavity of the metal mold to cast an outer race. As a result, an outer race holding an inner race therein is cast, and such an inner race is put in an inseparably sealed condition with respect to an inner portion of the outer race. The resin liner put on the inner race contacts the convex surface thereof closely owing to a casting pressure, and a clearance between the inner race and resin liner is thereby eliminated. On the other hand, the resin liner is put in a fused state with respect to the outer race, and the inner race alone becomes capable of contacting the resin liner slidably without any clearance therebetween. Thus, the rotating or swinging movement of the inner race with respect to the outer race in the spherical bearing disclosed in the same publication can be made practically without rattle.
In order to produce such spherical bearings in large quantities and reduce the manufacturing cost, it can be said that molding a cylindrical resin liner directly on a spherical surface of an inner race by injection molding with an inner race used as a core, and not putting a cylindrically molded resin liner on a convex surface of an inner race is preferable. Namely, in a preferable procedure for manufacturing a spherical bearing, a resin liner is put on the convex surface of an inner race directly first by injection molding with an inner race used as a core, and this resin liner-carrying inner race is thereafter placed as a core in a metal mold to cast an outer race as mentioned above. According to such a method, the resin liner comes into close contact with the convex surface of the inner race in a stage of completion of the molding thereof, so that the eliminating of a clearance between the resin liner and inner race can be done more easily.
When the above-mentioned inner race makes swinging movements repeatedly at a high speed with respect to the outer race, it is predicted that the temperature of the resin liner becomes high due to the friction between the resin liner and inner race. Therefore, it can be said that such a resin liner be formed preferably by using a thermosetting resin for the purpose of preventing the resin liner from being softened when the temperature is high.
However, when a resin liner is injection molded by using a thermosetting resin, it is necessary to maintain the resin liner, which has just been injection molded, at a temperature not lower than a predetermined level for a predetermined period of time, and thereby promote the turning of the thermosetting resin into a three-dimensional macromolecular compound. For example, in order to injection mold a resin liner of around 0.8 mm in thickness out of a phenol resin, it is necessary that an inner race and resin liner be retained in a metal mold maintained at 170 to 200xc2x0 C. for around 10 to 20 seconds even after the injection molding is completed. Otherwise, it is impossible to completely polymerize and cure the phenol resin which turns into a resin liner. In short, when a thermosetting resin is used as a material for a resin liner, excessive manufacturing time corresponding to the retention time is necessarily spent due to a polymerization reaction, and this greatly hampers the improvement of the production efficiency and the reduction of the production cost.
Such problems are not peculiar to a spherical bearing but applicable to all sliding bearings of the type in which a resin liner is used to form the whole or a part of a sliding guide surface.
The present invention has been made in view of such problems, and provides a manufacturing method of a sliding bearing of the type in which a sliding guide surface is formed by using a resin liner, capable of being produced with a high efficiency without wasting time even when the resin liner is manufactured by injection molding a thermosetting resin, and capable in its turn of reducing the production cost.
Namely, the present invention is characterized in that it provides a method of manufacturing a sliding bearing having a first member provided with a sliding guide surface, a second member which is provided with a sliding guide surface slidingly contacting the sliding guide surface of the first member, and which can be moved relatively to the first member, and a resin liner provided on at least a part of the sliding guide surface of the second member and slidingly contacting the sliding guide surface of the first member, including a first step of forming a sliding guide surface on the first member, a second step of fixing a thermosetting resin, which is to form the resin liner by injection molding using a metal mold in which the first member is inserted as a core, on the whole region or a part of the sliding guide surface of the first member, and covering the sliding guide surface of the first member with the same resin by molding using a metal mold, a third step of thermally curing the resin liner with the heat working on the sliding guide surface of the first member, when molding the second member, and a fourth step of forming a very narrow clearance between the sliding guide surfaces of the first member and second member by applying an external force to the first member or the second member, and thereby enabling a relative movement of the second member with respect to the first member to be made.
According to the method constituted in this manner of the present invention, the thermosetting resin which is to form the resin liner is not subjected to an independent thermal curing process immediately after the completion of the injection molding thereof but subjected to a thermal curing process by utilizing the molding heat during the molding of the second member in a metal mold. Therefore, the resin liner molding operation in the metal mold and the thermal curing process for the resin liner progress at the same time in the same time zone. This enables the production time to be shortened as compared with a method in which the thermal curing time for the resin liner is provided between the step of injection molding the resin liner and that of molding the second member in the metal mold.